Q fever is an understudied and under diagnosed infectious disease caused by the Category B agent, Coxiella burnetii. C. burnetii is a highly infectious Gram-negative bacterium causing disease with as few as 1 - 10 microorganisms. Q fever is naturally transmitted via ingestion of unpasteurized dairy products or by exposure to infected aerosols, manifesting disease with flu-like systems, and despite antibiotic treatment, the success of the treatment is not guaranteed. Q-Vax, formalin-inactivated whole bacteria, is currently the only human vaccine used for Q fever, but not approved in the US. Pre-exposure to C. burnetii can result in adverse reactions to Q-Vax. Given these impediments, a need exists to develop an efficacious, preferably subunit vaccine that minimizes such reactivities. Protection to Q fever appears to be both antibody- and cellmediated immunity-dependent, with the expression of TLR2 and IFN-y being important for mediating protective immunity. In the previous application, efforts focused on identifying C. burnetii proteins that enable its survival in the host phagolysosome as vaccine candidates. This approach has been successfully used in selecting similar vaccine candidates for brucellosis. Using this approach, 5-8 new vaccine candidates have been identified and vaccination with the collective recombinant proteins confers protective immunity against C. burnetii Nine Mile phase I challenge. To forward this effort, studies in Specific Aim 1 will optimize the vaccine formulation by testing different adjuvants and routes of delivery to optimize protective immunity that induces IFN-y and confers protective immunity. Studies in Specific Aim 2 will adapt these vaccines to our nasal delivery platform to enhance mucosal immunity to protect against pulmonary challenge. Studies in Specific Aim 3 will test the efficacy of these candidates against pulmonary challenge in both mice and guinea pigs. Phase I C. burnetii will be provided by Core B, the Coxiella Core;interactions will occur with Project 1.2 for Th1 and Th17 adjuvant discovery and Project 1.1 for optimizing pulmonary immunity to C. burnetii. We hypothesize that we can derive <8 candidates that can be formulated for eventual development of a Q fever vaccine. This research project fits within the RMRCE Integrated Research Focus on Immunomodulation, Adjuvants, and Vaccines, and will interact with RP 1.1 and RP 1.2 and utilize the resources of Coxiella Core.